I've been here for about 3 yrs now but can't honestly remember reading your past question on the center bearing. I do believe that the part from Volvo, like if it were a newer car and still under warranty does indeed only come from Volvo as a complete driveshaft assembly (or did, should re-check that) BUT most older Volvo techs have certainly diagnosed and replaced driveshaft center bearings on older Volvos and should even think of subletting the job to a driveshaft shop if the part isn't normally available from Volvo vs charging a customer major $$$ for a costly driveshaft. I don't believe that I've seen a bad center bearing on a XC but I've h ard years ago that some have failed causing vibrations through the grapevine (only).
As for the front viscous coupler bearing, there's a TSB or TNN (in Volvos tech data base) that explains the proceedure on how to replace that bearing and I've replaced those before. Any Volvo tech should be aware of that vs just wanting to replace that costly part.
It's too bad that you've had that much trouble getting your car fixed but problems like that shouldn't be typical anywhere.
As for AWD Volvos, I'm not a big fan of those either nor do I recommend them to anyone, at least not until the new Haldex systems came out. If you havent yet needed to replace your bevel gear, you're lucky but then perhaps you're the rare type who always runs 4 good tires (all the same) and have never needed to use your spacesaver spare (certain death to the bevel gear if driven too long and/or too fast and those are both very low #s).